Perfect Colors?

Okay, so let's say that you have an image file with an embedded color profile, a properly-profiled monitor, and an application that respects both profiles: will you finally see the proper, true colors?

Maybe.

First, you must define “true color.” If you define it as the colors as encoded in the image, then you'll see them properly to the extent that your monitor can actually display the image's full range of colors. A monitor or printer can only produce the colors, that, er, it has the physical ability to produce. If it's a particularly wide color space, and not a particularly high-caliber monitor, colors will be clipped in the process of display.

If you define “true color” as those colors as they existed when the camera first attempted to capture them, you have many, many more variables. These include the characteristics of the camera's sensor, the white-balance settings (and other settings such as exposure and saturation), the color space used to encode the image (are true colors clipped to fit inside the color space? Do true colors need to be “fudged” so that they match a color actually encodable within the space?), and any lossy compression used to encode the image.

Of course, even if you could see the true colors, you still might not like the image — in the end, there's no accounting for artistic taste :-)

Suggestions for the Digital Photographer

The two most important recommendations:

1. Embed color profiles in all images. This lets color-managed systems know exactly how to treat the color data in your image.

2. When preparing a photo for web display, use sRGB. On average, it's the closest color space to the average user's average monitor.... on average. Browsers that don't understand the embedded profile are all Color Stupid, so sRGB is the best you can guess.

If you want to maintain maximum quality and your camera has the ability to shoot raw images, do that, converting to a JPG, TIFF, or the like when needed, using a color space that's appropriate to the intended use (e.g. sRGB for the web, or for printing, the color space that best suits your printer). Investigate Apple's Aperture and Adobe's Lightroom. When writing images, be sure each includes an embedded color profile.

If you must (or prefer to) shoot JPG in the camera, use AdobeRGB or other “wider” color space, if available. When making copies for the web, or to give to technically-challenged friends and family, convert a copy to sRGB, embed a color profile, and use that. When working with the image in an editor like Photoshop, set the “working space” to a color space which encompasses both the image's native color space and the color space you intend to convert to.

Suggestions for the Internet Surfer

1. Understand the capabilities of your browser/OS (and perhaps make a change if you don't like the limitations).

2. Even if you don't normally use Apple's Safari, consider having it around for the times when you want to see profiled images at their best.

3. Profile your monitor so that you get the most proper colors it has to offer.

4. Beg Microsoft and Firefox developers to make their browsers color managed.

Suggestions for the Web Designer

CSS is, by definition, to be rendered with the sRGB color space, but this does not happen on any browser that I know of — for all practical purposes, they render CSS colors (and Flash, for that matter) without color management. On most browsers, this is the same treatment as images, but on Safari and other color-managed browsers that respect an embedded color profile, be sure to omit the profile if you want your image colors to match your CSS/Flash colors

This puts you directly at odds with getting the most proper colors, as that requires the embedded profile. Luckily, you can make the decision on a per-image basis:

• If you want the image colors to match CSS/Flash colors: save as sRGB without a color profile.
• If you want the image colors to look correct: save as sRGB with a color profile.

Thus, images that are part of the masthead or nav or other helper images can leave off the color profile, but photographs should keep them.

Suggestions for the Software Developer

The makes of browsers, image-display applications, image editors, and image-printing applications would do well to...

1. Recognize and apply embedded color profiles.

2. If an image has no profile, but is tagged as sRGB with the EXIF:ColorSpace tag, use sRGB. All digital cameras that I know of write sRGB color data without an embedded color profile, but they do note sRGB in this Exif field.

3. If no profile and no ColorSpace field, respond to the InteroperabilityIndex field (“R98” for sRGB, “R03” for AdobeRGB). This is from an Exif-related extension to JEITA's DCF ("Design rule for Camera File system") standard.

4. If all else fails, use a default color space that is initially sRGB, but allow the user to change it to whatever color space they like.

5. Educate your users about color-space issues.

Furthermore, software that writes images....

• When the color space is sRGB, include the sRGB profile and set the following Exif tags:

      ColorSpace = 1;
      InteroperabilityIndex = 'R98';
      InteroperabilityVersion = '0100';
  

• When the color space is Adobe RGB, include the Adobe RGB 1998 profile, and set the following Exif tags:

      ColorSpace = 65535;
      InteroperabilityIndex = 'R03';
      InteroperabilityVersion = '0100';
  

• When the color space is anything else, include the appropriate ICC profile and set the following Exif tags:

      ColorSpace = 65535;
      delete the InteroperabilityIndex field
      delete the InteroperabilityVersion field
  

Additionally, when changing the color space of an image, it would be a good idea to remove any MakerNotes fields related to the original color space, since they'll no longer apply.

Suggestions for Camera Makers

1. Embed a color profile in all images your cameras create.

2. For the time being, continue to default to using sRGB, but offer better color spaces as options.

3. Offer a color space that preserves as much color data as the camera's sensors originally capture (such as raw).

4. Educate your users about color-space issues.

Suggestions for Online Image Hosting Services

1. Add the appropriate color profile to unprofiled images that are tagged with a color space name.

2. Warn users when they upload images that are neither profiled nor tagged with a color space name.

3. When resizing images for thumbnails and such, convert to sRGB and embed a color profile.

4. Educate your users about color-space issues.

Links

Some related links that I found to be useful...

• William Steer's Introduction to Color Science
• Bruce Lindboom's RGB color-space info (detailed and technical)
• Charles Poynton's Color FAQ and Gamma FAQ
• Eugene Vishnevsky's Introduction to Color (a bunch of fun Java applets for interactive investigation)
• Comparisions of Adobe RGB and ProPhto RGB: one, two
• Ask a Color Scientist!
• Color-Science Glossary
• Online Exif-Data Viewer
• Norman Koren's Introduction to Color Management and Color Science
• ICC Profiles: v2 vs. v4
• JEITA's EXIF Standard (Ver 2.1)
• JEITA's DCF Standard (Ver 1.0)
• More on Digital Color Spaces: a Reply to Chris MacAskill